This application is based on Patent Application No. 11-360371 filed in Japan, the content of which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to an actuator using a displacement element such as a piezoelectric element and the like.
2. Description of the Related Art
In the field of actuators using a displacement element such as a piezoelectric element, the object of improving drive efficiency has resulted in the proposal of actuators which drive a displacement element such as a single plate piezoelectric ceramic or the like to oscillate an elastic member at a resonance frequency, and actuators which drive a laminate-type displacement element formed of laminations of a plurality of piezoelectric ceramic thin plates itself at a resonance frequency.
When the former single plate displacement element is used, there is scant internal loss of the displacement element itself, since the drive force generated by the displacement element is transferred to the elastic member without attenuation. Accordingly, the drive efficiency is high. However, since the total surface area of the displacement element is small and the impedance is high, the drive voltage must be increased in order to increase the output. Particularly when used in a portable device, several batteries must be used, or a booster circuit must be used. For this reason such a solution is contrary to the demand for lower cost and more compact and lighter weight devices.
When the latter laminate-type displacement element is used, the total area of the displacement element is increased by the laminate plates, and impedance is reduced by the resonance, such that a large output can be obtained using a low drive voltage. However, there is a large internal loss due to use of electrodes and adhesive between each piezoelectric ceramic thin plate. Accordingly, there is an increased attenuation of the drive force generated by the displacement element, and relatively low drive efficiency. Furthermore, when used in portable devices, the battery consumption is comparatively rapid, necessitating frequent battery replacement.
An object of the present invention is to provide an improved actuator.
Another object of the present invention is to provide an actuator using a low drive voltage and low power consumption.
A still further object of the present invention is to provide an actuator having a high drive efficiency.
These and other objects are attained by one aspect of the present invention providing a displacement element for generating a specific displacement by piezoelectric effect, a displacement expander for transmitting the displacement of the displacement element and expanding this displacement, a transmitter for transmitting the displacement expanded by the displacement expander to a driven member, and a presser for pressing the transmitter against the driven member, wherein the oscillation of the displacement element is restrained by the oscillation of the displacement expander.
The spring constant of the displacement expander is desirably less than the spring constant of the displacement element.
It is further desirable that the displacement element is driven by a drive signal of a frequency near the simple natural frequency of the displacement expander.
It is still further desirable that the displacement element is a laminate-type piezoelectric element.
In this way the actuator of the present invention sets the phase of the electromotive force to the reverse of the phase of the drive signal by piezoelectric effect of the piezoelectric element, thereby making it possible to reduce the drive voltage.
The displacement of the displacement element can be expanded by the displacement expander by setting the spring constant of the displacement expander smaller than the spring constant of the displacement element, thereby making it possible to obtain a greater output with less power consumption.
The current flowing to the displacement element can be minimized by driving the displacement element by a drive frequency of a frequency near the simple natural frequency of the displacement element, thereby minimizing power consumption.
The displacement element formed as a laminate type piezoelectric element, thereby allowing reduction of the drive voltage of the displacement element.